1. Field of the Invention
The present invention relates to a coil inductor, and more particularly to a coil inductor employed in an electric circuit such as a filter circuit or an oscillation circuit.
2. Description of Related Art
A copper wire which is covered with an insulating coat such as polyurethane has been used as a coil of a coil inductor. After the wire is coiled, the insulating coat of the wire is partly removed at an end, and the bare end of the copper wire is soldered to a terminal (or an electrode).
The coil, particularly the copper wire is thinned, when the inductance is wanted to be increased, or the inductor is wanted to be more compact. However, since copper is diffusible into solder, using an excessively thinned wire causes a problem that the copper partly diffuses into the solder to breaking of the wire when the wire is connected to the terminal (or the electrode) or when the inductor is mounted on a printed-wiring board by soldering. Therefore, the diameter of the copper wire had to be kept approximately 50 .mu.m at the minimum, and could not be thinned more.